Killer B Motorsport 4-1 Holy Header Exhaust Manifold DIY Rotated 2002-2014 WRX / 2004-2021 STI

The Killer B Motorsport Holy Header was developed using state of the art CAD software & simulations to determine optimal design to increase power in the mid to high RPM range. Short as possible primaries with a single secondary significantly decrease header volume allowing exhaust gas pressure to build quickly. Symmetrical 4-1 design maintains high and consistent exhaust velocity as RPMs rise. You can expect faster spool up time compared to long primary/double secondary designs. A difference you will immediately notice in throttle response and the ability to hold more power higher into the revs.

This is a DIY kit, you will have to construct the uppipe to your needs! If you are looking for a direct replacement header please use Killer B's other header listings which can be found on our site.

Features include:

• Short Equal Length Primaries. The shortest possible length primaries you can have on an Equal Length header. Short means less header volume and quick spool up.
• Symmetrical Primary Design. All primaries have a similar tube length AND bend geometry. This keeps the pulse velocities high and consistent compared to equal length headers with different (non-symmetrical) primary tubing geometry. 
• Smooth Mandrel Bends. All of the bends utilize a mandrel for smooth non-restrictive flow. Not only that, they use the largest bends possible at every location. It would be cheaper to use 2” bends everywhere, like others do, but that’s not going to give the best performance. 
• Thick Walled 321 Stainless Steel Construction for Long Life. 321 is alloyed with titanium, costs more, a lot more, but it’s the ideal material for high temperature turbocharged applications. Would 304 stainless work, yes, but the temperatures on turbocharged cars can exceed the limits of 304 stainless enough to make them brittle and crack. 321 stainless steel has higher strength and toughness at elevated temperatures. It was developed by the aircraft industry specifically to address 304 stainless manifolds that were cracking. Killer B Motorsport is the only company that manufactures full 321 headers. 
• High Heat Retention. 321 stainless steel conducts less heat than 304 stainless steel. The short primaries and properly sized secondary’s also pull less heat from the exhaust gasses increasing turbine efficiency. Large tubing headers expose the exhaust gasses to more surface area transmitting more heat and reducing exhaust energy. You can also ceramic coat or wrap the headers (and keep the warranty) without exceeding the temperature range like you can with 304 stainless. 
• Up-Pipe to Manifold V-Band Included (not welded) 
• Includes Non-Trimmed or Welded 321 Stainless Steel Up-Pipe. 
• No Turbo Flange Provided 
• Works with OEM EJ25 Oil Pans, and Killer B Motorsport Performance Aluminum Oil Pan! 
• No Accommodations for External WasteGate Included 
• Allows placement of Up-Pipe to Accommodate nearly any Rotated Turbocharger setup 
• DIY Reduced cost!
• Works with OEM EJ25 Oil Pans, and Killer B Motorsport Performance Aluminum Oil Pan! 
• Made in the USA and Killer B quality!
• NOTE: 2002-2005 WRX Requires EJ25 Oil Pan
• NOTE: May require slight modifications to the stock oil cooler for 06-07 WRX and Forester XT models. Some models may require modification to the stock fan shroud.